MRK, Daiichi's ADC Drug Gets FDA Breakthrough Tag for Ovarian Cancer

Merck (MRK) and its Japanese partner Daiichi Sankyo announced that the FDA has granted Breakthrough Therapy Designation ("BTD") to their investigational pipeline candidate, raludotatug deruxtecan (R-DXd). The regulatory body granted a BTD to R-DXd for treating platinum-resistant epithelial ovarian, primary peritoneal, or fallopian tube cancers that express CDH6 in adult patients who have previously received treatment with Avastin (bevacizumab).

A first-in-class CDH6-directed DXd antibody-drug conjugate ("ADC"), R-DXd, is being jointly developed by Merck and Daiichi Sankyo.

The FDA’s BTD is a process that speeds up the development and review of drugs for serious or life-threatening conditions. This designation is granted when early clinical evidence suggests that a drug candidate may significantly improve over existing treatments on one or more key clinical measures.

The BTD was based on data from the ongoing phase II/III REJOICE-Ovarian01 study and a phase I study, which evaluated R-DXd in the given patient population. Data from the REJOICE-Ovarian01 study is expected to be announced at an upcoming medical conference.

MRK's Price Performance

Year to date, shares of Merck have plunged 18.5% compared with the industry’s decline of 0.1%.

MRK’s Daiichi's Deal for R-DXd & Other ADC Candidates

Merck acquired global co-development and co-commercialization rights to R-DXd and two other ADCs, patritumab deruxtecan and ifinatamab deruxtecan, from Daiichi Sankyo in October 2023 for a total potential consideration of up to $22 billion. However, Daiichi Sankyo has retained exclusive rights for the development of the candidates in Japan.

In August last year, Merck expanded the collaboration to co-develop and co-commercialize MK-6070, an investigational T-cell engager targeting delta-like ligand 3 (DLL3), which it obtained from its recent acquisition of Harpoon Therapeutics.

Ifinatamab deruxtecan is being developed in separate phase III studies for treating small cell lung cancer, esophageal cancer and prostate cancer. The ADC candidate is also being evaluated both as monotherapy and in combination with other therapies in several early-to-mid-stage studies for treating various other solid tumors, including extensive-stage small cell lung cancer.

Patritumab deruxtecan is being developed in late-stage studies for treating certain patients with breast cancer.

The FDA’s Breakthrough Therapy status for R-DXd marks the second BTD received under the Merck and Daiichi Sankyo collaboration, the first being granted to ifinatamab deruxtecan for treating certain patients with extensive-stage small cell lung cancer last month.

MRK’s Competition in the Evolving ADC Space

ADCs are being considered a disruptive innovation in the pharmaceutical industry, as these will enable better treatment of cancer by harnessing the targeting power of antibodies to deliver cytotoxic molecule drugs to tumors.

Daiichi Sankyo has several ADCs in clinical development across multiple types of cancer. It markets Enhertu, a HER2-directed ADC, in partnership with AstraZeneca AZN, which is presently approved across multiple indications, including HER2-mutated breast, lung and gastric cancers.

The FDA approved AZN and Daiichi’s second ADC drug, Datroway, for treating unresectable or metastatic HR-positive, HER2-negative breast cancer in January 2025. The regulatory body approved Datroway for its second indication, non-small-cell lung cancer, in June.

Pfizer PFE also tapped into the lucrative ADC space with the acquisition of Seagen for $43 billion in late 2023.

Following this acquisition, PFE added four ADCs to its portfolio — Adcetris, Padcev, Tukysa and Tivdak — all approved across various types of solid tumors and hematologic malignancies. These products contributed meaningfully to Pfizer’s revenues in the first half of 2025.

MRK’s Zacks Rank

Merck currently carries a Zacks Rank #3 (Hold). You can see the complete list of today’s Zacks #1 Rank (Strong Buy) stocks here.

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This article originally published on Zacks Investment Research (zacks.com).

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